Former Rep. Barney Frank, a liberal icon who was a key architect of the landmark Wall Street regulations Democrats enacted in the wake of the 2008 financial crisis, has entered hospice care at his home in Maine. And as one of his last acts, he is preparing to release a book repudiating his party’s left flank. A champion of liberal causes during his 32 years representing Massachusetts in the House, Frank says progressive Democrats have “embraced an agenda that goes beyond what’s politically acceptable.” “Until we separate ourselves from that agenda, we don’t win,” he said in an interview Tuesday.